Sharif Digital Repository

Objectives: The aim of this study was to assess and compare the crystalline structures of both powder and bulk human dental enamel by X-ray diffraction analysis (XRD). Methods: The buccal surfaces of 60 selected noncarious third molars were divided into two groups of powdered and bulk enamel specimens. To prepare enamel powders, the enamel tissues were ground and powdered manually using a mortar and pestle. For bulk samples, the enamel slabs were sectioned using a low-speed diamond saw. The crystalline structures of samples were analyzed by XRD, and the obtained data were analyzed. The values of the lattice parameters were obtained using the equation of hexagonal crystalline structures. The... 

Variable reluctance (VR) resolver is an angular position sensor, which is commonly used in the automotive industry. In this article, a general method for determining the winding configuration of VR resolvers is proposed, which eases the manufacturing process. At first, the operational principle of conventional winding has been presented using mathematical formulations. Following that, the nonoverlapping tooth coil winding method, as the ideal winding option for VR resolver, has been extended, which can be applied to the VR resolver with arbitrary poles and stator tooth numbers. The method of determining the reference and signal windings presented and used to determine the winding for a two,... 

Introduction - This study aimed to compare the amount and pattern of stress and strain distributed around periodontally compromised splinted teeth and the two-implant abutments supported six-unit fixed partial denture (FPD) using finite element analysis (FEA). Methods and Materials - Six mandibular anterior teeth of a dental model were scanned and the scans were transferred to 3D CAD design and finite element software. Jaw bone was also designed and the teeth were splinted by fiber-reinforced composite (FRC) band. In another model, two implants were placed at the site of canine teeth and a six-unit FPD was designed over them. Models were transferred to finite element software and after... 

This article presents a new method for determination of meshing stiffness of the gear teeth using three dimensional analysis of tooth stiffness. The teeth are treated as explicit capacitive fields and their compliance matrix is determined by considering virtual interconnected springs located at defined nodes on tooth profile. The stiffness of any arbitrary point on the profile can then be determined as a linear function of neighboring nodes stiffness. The results of this analysis help in determination of load distribution for a pair of meshing gears under real operation conditions where deflections and misalignments are inevitable. Copyright © 2005 by ASME  

Variable reluctance resolver (VR-Resolver) is a robust electromagnetic sensor that provides position information for closed-loop control systems of permanent magnet synchronous motors (PMSMs). For specific motion control applications, an outer rotor structure is presented for the VR-Resolver in this article with a nonoverlapping tooth-coil windings configuration to simplify the manufacturing process. The study on the structure of the proposed position sensor is carried out, followed by the description of the working principle. The presented outer rotor VR-Resolver is simulated and its performance is investigated in detail with the aid of transient finite-element analysis (TFEA). Sensitivity... 

Purpose: Quantification of teeth is of clinical importance for various computer assisted procedures such as dental implant, orthodontic planning, face, jaw and cosmetic surgeries. In this regard, segmentation is a major step. Methods: In this paper, we propose a method for segmentation of teeth in volumetric computed tomography (CT) data using panoramic re-sampling of the dataset in the coronal view and variational level set. The proposed method consists of five steps as follows: first, we extract a mask in a CT images using Otsu thresholding. Second, the teeth are segmented from other bony tissues by utilizing anatomical knowledge of teeth in the jaws. Third, the proposed method is followed... 

Variable Reluctance (VR) resolver is an angular position sensor that is commonly used in the automotive industry. In this paper, A general method for determining the winding configuration of VR resolvers is proposed, that eases the manufacturing process. At first, the operational principle of conventional winding has been presented using mathematical formulations. Following that, the non-overlapping tooth coil winding method, as the ideal winding option for VR resolver, has been extended that can be applied to the VR resolver with arbitrary poles and stator tooth numbers. The method of determining the reference and signal windings presented and used to determine the winding for a 2, 6, and 8... 

We produced bifurcated bone-like shape memory implant (BL-SMI) with desirable tooth-root fixation capability by compact-sintering of TiH2–Ni-urea mixture. The primary constituents of the porous product were Ni and Ti. We could adjust the pores' shape, size, and interconnectivity for favorite bone ingrowth by using urea as a space holder. Without urea, we obtained an average porosity of 0.30, and a mean void size of 100 μm. With 70 vol % urea, we got 62% interconnected pores of 400 μm average size. Aging allowed us to tune the austenite-martensite transformation temperatures towards the needed body tissue arouse. Differential scanning calorimetry measured the transformation temperatures.... 

Nerve repositioning surgery is one of the treatments chosen for the patients with edentulous posterior atrophic mandible. Like any other treatments, this therapy has its advantages and disadvantages, indications and contraindications. The most important complication of this procedure is neurosensory disturbance. This problem may occur at different stages of the treatment. One common time when nerve damage happens is when the nerve is located outside the canal and drilling and insertion of the implant are performed. Accordingly, this report describes a simple and feasible method to retract and protect nerves outside the canal during the treatment of nerve transposition. This will reduce the... 

This article presents a method for determination of meshing force distribution on contact region of spur gear teeth. In this method it is assumed that there are inter-connected springs on the teeth profile. These springs treat as capacitive fields. The compliance matrices of these fields are determined from the results of finite element analysis done on 3-D model of a gear. The tooth compliance matrix is used as a reference data to determine the tooth deformations for any meshing situation. The meshing force distribution is calculated using this reference data and Hertz theory for contacting bodies. The results of this analysis help in stress analysis under real operation conditions and more... 

This study reports on the simulation of temperature distribution of human tooth under a laser beam based on non-Fourier models. The temperature in the tooth depth that directly results from the conduction heat transfer process is caused by the lengthy thermal relaxation time in the tooth layers. A detailed tooth composed of enamel, dentin, and pulp with unstructured shape, uneven boundaries, and realistic thicknesses was considered. A finite difference scheme was separately adopted to solve time-dependent equations in solid layers and soft tissue of the tooth. In this study, a dual-phase-lag non-Fourier heat conduction model was applied to evaluate temperature distribution induced by laser... 

There are numerous functions for laser in modern implant dentistry including surface treatment, surface coating, and implant manufacturing. As laser application may potentially improve osseointegration of dental implants, we systematically reviewed the literature for in vitro biological responses to laser-modified or processed titanium dental implants. The literature was searched in PubMed, ISI Web, and Scopus, using keywords “titanium dental implants,” “laser,” “biocompatibility,” and their synonyms. After screening the 136 references obtained, 28 articles met the inclusion criteria. We found that Nd:YAG laser was the most commonly used lasers in the treatment or processing of titanium... 

This study aimed to investigate the changes in crystalline structure and resistance to demineralization of human dental surface enamel treated with erbium-doped yttrium aluminium garnet laser (Er:YAG) laser and fluoride. The enamel surfaces were divided into four groups according to the treatment process including, (L): irradiated with Er:YAG; (F): treated with acidulated phosphate fluoride gel (LF): Pre-irradiated surfaces with Er:YAG subjected to acidulated phosphate fluoride gel and (FL): laser irradiation was performed on the fluoridated enamel surface. Before and after the treatment procedure, the samples were evaluated using X-ray diffraction, scanning electron microscope (SEM) and the... 

Resolvers are widely used in high performance motion control of inverter-driven motors. Among different types of resolvers, axial flux wound-rotor (AFWR) resolvers have gained more attention due to their higher stability against static eccentricity. So, in this study the influence of stator and rotor winding arrangements on the accuracy of AFWR resolvers is presented. A single/two phase distributed, constant turn winding is considered for the rotor and the influence of short circuit damper winding of the rotor is investigated. For the stator, constant turn, distributed winding and variable turn, on-tooth winding is examined. Finally, it is shown that using variable turn on-tooth winding for... 

Introduction: In recent years, artificial intelligence (AI) has been applied in various ways in medicine and dentistry. Advancements in AI technology show promising results in the practice of orthodontics. This scoping review aimed to investigate the effectiveness of AI-based models employed in orthodontic landmark detection, diagnosis, and treatment planning. Methods: A precise search of electronic databases was conducted, including PubMed, Google Scholar, Scopus, and Embase (English publications from January 2010 to July 2020). Quality Assessment and Diagnostic Accuracy Tool 2 (QUADAS-2) was used to assess the quality of the articles included in this review. Results: After applying... 

Periodontitis is a common oral disorder leading to tooth loss in both developed and developing regions of the world. This multifactorial condition is related to the abnormal activity of several molecular pathways, among them are oxytocin-related pathways. In this study, we enrolled 26 patients and 28 controls and assessed the expression of four oxytocin-related genes, namely, FOS, ITPR, RCAN1, and RGS2, in circulation and affected tissues of enrolled individuals using real-time PCR. Expression of FOS was downregulated in total periodontitis tissues compared with total control tissues [ratio of mean expression (RME) = 0.23, P-value = 0.03]. Expression of FOS was also lower in total blood... 

High pole number permanent magnet (PM) motors, due to their high torque density, have been receiving considerable attentions in recent years. To achieve an accurate position control in PM machines, resolvers are suggested for industrial applications. Mechanical and electromagnetic considerations in the case of high pole number resolvers lead the machine designers to choose small cores with low slot numbers. This paper proposes two different on-tooth winding configurations to achieve high pole number without increasing the slot numbers, while the accuracy of the detected position is intended to be the maximum value. Variable turn on tooth winding (VTTW) is compared with fractional slot...